These very small flies are cosmopolitan, and
are usually known as vinegar flies. They are so small that they can pass
through ordinary “flyscreen,” and are therefore common pests in homes,
restaurants, fruit markets, canneries, cellars, or basements containing
fermenting liquids (vinegar, cider, wine, beer), and in other places that
contain attractive food materials.
Description.
All the economically important species are
superficially similar in Appearance. They are dull brownish yellow or brownish
black in their over-all aspect. A feathery bristle on the antenna helps to
distinguish Drosophila from other small flies. The adult of the best-known
species, D. melanogaster Meigen is 3 mm long, with red eyes, tan-colored
head and thorax, and the abdomen is blackish on top and grayish underneath.
Other species that commonly become pests are:
- D. funebris (F.),
- D. repleta Wollaston,
- D. buschii Coquillett,
- D. affinis Sturtevant,
- D. falleni Wheeler,
- D. tribunctata Loew, and
- D. hydei Sturtevant.
Life Cycle.
Vinegar flies lay their eggs near the surface
of fermenting or rotting fruit and vegetable material or in unclean garbage
cans. The pearly-white, cylindrical eggs, which can be observed with a hand
lens, have 2 to 4 threadlike filaments at one end, and these filaments protrude
above the liquid material in which the eggs are laid.
The tiny maggots crawl out of the liquid food to some drier substance,
preferably loose soil, to pupate. The brown, seed-like pupae have 2 hornlike stalks
at the anterior end. About 500 eggs are deposited by a single female, on an
average, and since the life cycle may require only 8 to 10 days in warm
weather, the reproductive potential is enormous.
Control Tactics:
The most important aspect of Drosophila
control is the elimination of food and breeding sources. This refers not only
to the most obvious materials, such as piles of rotting and fermenting fruits
and vegetables, but also to such sources as peelings accidentally swept under
appliances or counters, discarded ketchup or milk bottles that have retained a
portion of their contents, dishwater or water from floor mappings that has
seeped into crevices, garbage-laden water from sinks, or a foul, soured mop.
Vinegar flies constitute a serious problem in
rural communities that are close to extensive sources of the insects, such as
tomato fields or canning plants. Cannery sanitation is extremely important. Egg deposition in boxes of tomatoes in the field
or on pallets in the receiving stations of canneries can be prevented for a
24-hour period by the application of pyrethrum dust, principally because of its
repellent effect (Stombler et al., 1957).
Piles of culled fruit are important sources of vinegar flies and dried fruit beetles (Carpophilus spp.). These pests can be controlled by suitable insecticides, such as liquid sprays or
granular formulations. Insecticide granules have to be mixed into the mass of
fruits if the pile is more than 24 in. (60 cm) deep. Larvae can be prevented from
developing long enough for the fruit wastes to become too dry to attract
insects. Sprays of Tempo 20 WP have been found to be effective. For control of
vinegar flies in wine cellars, an aerosol of 3% pyrethrins, combined with
piperonyl butoxide as synergist, was found to be effective, but treatments once
or twice daily were required to keep the insects under control (Yerington,
1971).
Substantial reduction in vinegar fly populations in tomato fields was obtained by releasing
large numbers of the adult flies of both sexes that had been sterilized with 1%
aqueous apholate, a well-known insect chemosterilant. The investigators stated
that release of sexually sterilized flies in a program such as they described
“shows promise of controlling D. melanogaster in commercially grown tomatoes,
especially if the program is conducted on a community-wide basis” (Mason et
al., 1968). In the home, space sprays, aerosols, as they would be used for
house fly control, have been effective against vinegar flies.
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